Former Kincora residents, from left to right, Richard Kerr, Gary Hoy, and Clint Massey. At least 29 boys were abused at the East Belfast home.
Photograph: Brian Lawless/PA

An inquiry into child abuse across a range of institutions in Northern Ireland will focus on Tuesday on the Kincora boys home scandal including allegations that MI5 blackmailed a paedophile ring which operated there in the 1970s.

The historical institutional abuse inquiry will hear evidence from men who were abused at Kincora when they were children and their allegations that the perpetrators were protected because they were state agents spying on fellow Ulster loyalists.

A number of Kincora abuse victims have tried through the courts to force the scandal to be included in the national investigation into allegations of establishment paedophile rings operating in Westminster.

Gary Hoy tried and failed last month to force the home secretary to include Kincora in the Westminster inquiry. Hoy and others fear that the Kincora inquiry, which is based in Northern Ireland and taking hearings at the court in Banbridge, County Down, will not have access to sensitive MI5 intelligence files on the people who ran Kincora.

Amnesty International has described the Kincora scandal as one of the most disturbing to emerge from the Ulster Troubles.

Patrick Corrigan, Amnesty’s director in Northern Ireland, said: “Nothing less than a full public inquiry – with all the powers of compulsion which that brings – can finally reveal what happened and the role that the security services may have played in the abuse of these vulnerable boys.”

At least 29 boys were sexually abused by Kincora housemaster and prominent Orange Order member William McGrath and others at the east Belfast home. One boy is said to have committed suicide following years of abuse by jumping off a ferry into the Irish Sea in the late 1970s.

Another of the abuse victims at Kincora, Clint Massey, told the Guardian last year that he even tried to file a report at a local police station in east Belfast about what was happening to him and other boys at the home in the mid-1970s. However, Massey said he was forcibly marched out of the RUC station by police officers and that his complaint was not recorded.

Former army intelligence officer and whistleblower Colin Wallace has consistently claimed that MI5, RUC special branch and military intelligence knew about the abuse going on at Kincora and used it to blackmail the paedophile ring to spy on hardline loyalists.

In 1980, Wallace was arrested and convicted of manslaughter. He spent six years in jail despite suggestions he had been framed. His conviction for manslaughter was quashed in 1996 in the light of fresh forensic evidence and shortcomings at his trial. In 1990, Margaret Thatcher was forced to admit that her government had deceived parliament and the public about Wallace’s role.

An independent investigation by David Calcutt QC found that members of MI5 had interfered with disciplinary proceedings against Wallace. As a result, Wallace was awarded £30,000 in compensation.

Three men were jailed for their part in abuse at Kincora in 1981, but attempts to establish the truth about British state involvement have been blocked. It has persistently been alleged that McGrath, who was a leader in an extreme evangelical Protestant group called Tara, was an informant for British intelligence. McGrath was jailed for sexual offences in 1981 and is now dead.

Theresa May, the home secretary, has insisted that the chairman of the Banbridge-based inquiry, retired judge Sir Anthony Hart, will have full access to government and intelligence files relating to Kincora.

The historical institutional abuse inquiry is investigating 22 orphanages, care homes and other institutions where child sexual abuse took place. The inquiry team is expected to hear from around 450 witnesses, some of whom have travelled from as far as the United States and Australia to give evidence.